1. Field of the Invention
The present invention relates to a sensing element and a detecting device by using plasmon resonance, and a method for producing the sensing element. The present invention relates to a so-called biosensor with the use of a recognition capability peculiar to a substance of a biometric origin or a substance similar thereto.
2. Related Background Art
A biosensor is a measuring device making use of the excellent molecular recognition capability of living matter and a biomolecule. The living matter has a combination of substances having a mutual affinity with each other, such as an enzyme-substrate, an antigen-body and DNA-DNA. The biosensor makes use of a principle that one substance of the combination, which is immobilized or carried on a substrate, can selectively measure the other substance. In recent years, the biosensor has been expected to be widely applied not only to the medical field, but also, to fields of environment and food, so that a biosensor, which is installable everywhere or is transportable, is small and lightweight, has been expected, to be used in wider application areas.
Currently, as one of highly sensitive sensing systems, a sensor, using an interaction between plasmon existing on a metal surface and metallic microparticles and light, has been diligently studied.
A conventional sensor using surface plasmon resonance (SPR sensor) uses a phenomenon that when light is launched onto the surface of a metallic thin film, only light incident from a certain particular angle resonates with and is absorbed by plasmon on the metal surface, and the reflected light is attenuated. The angle at which the absorption occurs is sensitive to a surface condition (refractive index) of the metallic thin film, so that the sensor can measure a reaction (for instance, an antigen-antibody reaction) occurring on the metal surface by measuring the intensity of reflected light while changing the incidence angle.
However, the SPR sensor has had a problem of needing a prism from a structural standpoint, and consequently, making an optical system complicated. The SPR sensor also had a problem that it cannot be applied to a substrate with a curved surface, because of the need to prepare a metallic thin film by vacuum deposition, which limited the substrate and a device structure. Because of these problems, the SPR was considered to be difficult to miniaturize.
In such a background, Japanese Patent Application Laid-Open No. 2000-356587 proposed a sensor using localized surface plasmon resonance (an LSPR sensor) in metallic microparticles. The localized plasmon resonance sensor detects the refractive index of a medium around the metallic microparticles, by measuring an absorbance of light having been transmitted through the metallic microparticles, which are fixed like a membrane on a substrate surface.
Furthermore, Japanese Patent Application Laid-Open No. 2003-268592 discloses an invention of forming mutually isolated metallic particles in a plurality of pores in anodized alumina oxide for the purpose of regularly and independently arranging the metallic particles in an arbitrary uniform size and an arbitrary array, and using it for a plasmon resonance device.
Furthermore, Japanese Patent Application Laid-Open No. 2004-191341 discloses a molecule-recognizing element applicable to the biosensor, which is prepared by introducing a metallic material in columnar pores in a porous film formed on the substrate, preparing a columnar structure by removing the porous film and immobilizing a molecule-recognizing material on it. The above Japanese patent document also discloses that the metallic material may be introduced through electrodeposition (electrolysis plating).